The present invention relates to devices and techniques for measuring arsenic concentrations, and more specifically for quantitative measurements of arsenic concentrations in aqueous solutions. The invention may be used to measure arsenic concentrations in groundwater.
A devastating health crisis is currently unfolding in Bangladesh and West Bengal, India, due to arsenic enrichment of groundwater supplied by millions of tubewells and used for human consumption. See e.g., British Geological Survey/Mott MacDonald Ltd. (U.K.), “Groundwater studies for arsenic contamination in Bangladesh,” Final Report-Main Report, (1999). The arsenic enrichment is most, likely of natural origin. An estimated 25 million people are at risk of developing arsenic related health conditions that include skin lesions, respiratory illnesses and eye problems as early or intermediate disorders, as well as more deadly and debilitating long term diseases such as cancer of the skin, bladder, lung, and other internal organs, heart disease and neurological disorders. (See e.g., Chakraborty A. K. and Saha K. C., “Arsenical dermatosis from tubewell water in West Bengal,” Indian J. Med. Res., 85, 326-334 (1987); and Guha Mazumder D. N., Haque R., Ghosh N. et al. “Arsenic levels in drinking water and the prevalence of skin lesions in West Bengal,” India Int. J. Epidemiology, 27(5), 871-77 (1998). A number of governmental and non-governmental organizations are concerned about this mass arsenic poisoning related health crisis of unprecedented magnitude, and are seeking ways to address it (See e.g., van Geen, A., H. Ahsan, A. Horneman, R. K. Dhar, Y. Zheng, M. Stute, H. J. Simpson, S. Wallace, C. Small, M. F. Parvez, V. Slavkovich, N. J. Lolacono, A Gelman, M. Becker, A. Z. M. I. Hussain, H. Momotaj, M. Shahnewaz, K. M. Ahmed, and J. Graziano, “Well-switching: a remediation option worth promoting to reduce arsenic exposure in Bangladesh,” Bulletin of the World Health Organization, submitted May 2001.
The problem of arsenic contamination of the groundwaters, which is now well publicized in the case of Bangladesh or West Bengal, is not limited to those geographical regions. Arsenic contamination of groundwaters is also found, and is of concern in other regions of the world. See e.g., Smith A. H., Goycolea M., Haque R. et al. “Marked increase in bladder and lung cancer mortality in a region of northern Chile due to arsenic in drinking water,” Am. J. of Epidemiology, 147, 660-669 (1998).
A potential solution to alleviate the notable case of mass slow poisoning in Bangladesh and West Bengal, involves switching water consumption to safer wells that have no arsenic contamination or have arsenic contamination which is within acceptable “safe levels.” Other solutions may involve treating contaminated groundwater to remove arsenic to make the water fit for human consumption. Arsenic levels of less than 50 μg/L are considered safe under official Bangladesh drinking water standards. More recent guidelines from the World Health Organization (WHO) recommend that arsenic levels be below 10 μg/L arsenic. In any case, there is an urgent need to accurately measure the arsenic concentrations in well waters to identify those that are unsafe due to arsenic contamination, as well as to identify those that are safe for use. Any solution will require on-going monitoring of water quality in the field.
Unfortunately, the safe arsenic levels of at most a few tens of μg/L are below the detection limits of conventional arsenic measurement devices and techniques that may be available or amenable for field use. For example, the “Merck field kit” (sold, for example, by EM Sciences, Merck KGaA, Darmstadt, Germany) has been widely used to measure arsenic. The Merck kit has an effective detection limit of about 100 μg/L. The Merck kits, and all other field kits commonly used, for example, in Bangladesh, are based on a mercuric bromide stain method. The method involves reducing or converting inorganic arsenic in solution into arsine gas. The arsine gas is collected and reacted with mercuric bromide on an indicator test strip. The color of the test strip changes from white, to yellow, or brown, according to the concentration of arsine it is exposed to. Estimates of the arsine concentration are obtained by visually identifying the color of the test strips. However, the color sensitivity to arsine concentration is poor, resulting in high detection limits. Efforts have been made to modify the arsine collection and exposure methods, to reduce the detection limits and to increase the sensitivity of the method. Also, indicator test strip chemistries have been improved to broaden the range of color responses. Modified field kits that are now available may include standard color charts for visual comparison. However, none of the modified or improved field kits have been satisfactory in the field. The modified methods often are complex and difficult to implement. The methods still call for visual identification of indicator test strip colors. The color sensitivity of the indicator test strips varies with the level of arsenic being measured. Different test strips may have to be used for different arsenic ranges, making continual adjustment or recalibration necessary according to the level of arsenic in the specimen. Results for samples containing arsenic levels in the range of 10 μg/L to 100 μg/L, are generally considered suspect. Further, the kits still utilize the chemistry that produces highly toxic arsine gas.
Consideration is now being given to other methods of accurately detecting arsenic levels in water samples. Attention is directed toward producing a sensitive field kit for quantitative detection of arsenic that retains it sensitivity over the wide range of arsenic concentrations found in groundwater. Attention is particularly directed toward adapting known laboratory chemical analysis or assay methods that do not produce toxic arsine gas as a byproduct in the testing groundwater for arsenic.